1. Field of the Invention
The present invention relates to a toner, a method of manufacturing the same, a two-component developer, a developing device, and an image forming apparatus.
2. Description of the Related Art
Electrophotographic image forming apparatuses have been widely used as copiers so far, and in recent days, also as printers, facsimile machines, and the like apparatuses along with spread of computers since the electrophotographic image forming apparatuses operate excellently as output units for computer images created by computers. In a general electrophotographic image forming apparatus, a desired image is formed on a recording medium through a charging step of uniformly charging a photosensitive layer of a photoreceptor drum; an exposing step of irradiating signal light of an original image onto the surface of the charged photoreceptor drum so that an electrostatic latent image is formed thereon; a developing step of supplying an electrophotographic toner (hereinafter, simply referred to as “a toner”) to the electrostatic latent image on the surface of the photoreceptor drum so that the electrostatic latent image is visualized and a visible image is thus formed thereon; a transferring step of transferring the visible image on the surface of the photoreceptor drum onto a recording medium such as paper or OHP sheet; a fixing step of fixing the visible image onto the recording medium by application of heat, pressure, etc.; and a cleaning step of removing and cleaning by a cleaning blade the toner and the like remaining left over the surface of the photoreceptor drum after the visible image has been transferred. The visible image may be transferred onto the recording medium by way of an intermediate transfer medium.
In the meantime, various techniques related to computers have been further developed. For example, definition of computer images becomes higher and higher. This raises a demand on the electrophotographic image forming apparatus to form high-definition images almost equivalent to the computer images, which high-definition images reproduce tiny shapes, slight hue variation, etc. of the computer images precisely and clearly. In response to the demand, definition of the electrostatic latent image is further improved. In order to precisely reproduce a high-definition image with the improvement in the definition of the electrostatic latent image, there has been proposed various arts for precisely controlling characteristics of a developer adhered to a recording medium, such as an average particle size, a particle size distribution and a coloring property of the toner. Among these arts, many are particularly proposed to further improve image quality by decreasing the particle size of the toner, and various studies have been made for manufacturing a small-size toner. The small-size toner is useful for forming high-definition images. However, when the small-size toner contains a large amount of fine toner particles having a volume average particle size of 4 μm or less, for example, there is caused such a problem that flowability and transfer efficiency undesirably decrease, thus resulting in a failure to obtain an image of a sufficient quality.
In order to solve this problem, in the toner and the developer composition of Japanese Unexamined Patent Publication JP-A 9-114127 (1997), a toner having a volume average particle size of 3.0 μm to 9.0 μm is so regulated that a volume average particle size, a content of a colorant, and a weight of developed toner satisfy a predetermined condition, thus achieving a good balance between high image-quality and developing property (an appropriate density and prevention of fogs). However, in this case, JP-A 9-114127 discloses that in order to obtain an image of a higher quality, particle size distribution is set to D50P/D84P≦1.45.
Further, the image forming apparatus of Japanese Unexamined Patent Publication JP-A 2004-4974 is so designed as to be capable of forming a high-definition image on a recording medium, by using a color toner which is synthesized according to a polymerization method and in which the following expression is satisfied: 1.25≦Dn50/Dn25≦1.50 and a loose apparent density of the developer is set to be from 0.30 to 0.45 mg/cm3. Note that Dn25 represents a size at 25% of cumulative number and Dn50 represents a size at 50% of cumulative number.
Further, a toner having an average degree of circularity of 0.940 or less, for example, generally exhibits a good cleaning property since it is easily scraped by a cleaning blade. However, in this case, a decrease occurs in the efficiency of the transferring of the toner onto the recording medium, thus causing a failure to stably form a high-definition image. On the other hand, when the toner is close to a perfect sphere in shape, the transfer efficiency is high but the toner is difficult to be scraped by the cleaning blade, thus causing deterioration in cleaning property. Consequently, a design on a shape of the toner is important for obtaining a toner which exhibits a good cleaning property and excellent transfer efficiency and which can correspond to high-definition of the image.
In JP-A 9-114127 and JP-A 2004-4974, the particle size distributions of toner are so defined as D50P/D84P≦1.45, or 1.25≦Dn50/Dn25≦1.50. However, in the particle size distributions, the content of the fine toner particles having a volume average particle size of 4 μm or less is insufficient, thus causing a failure to obtain an image sufficiently improved in image definition and resolution.
Further, among the toner particles, particles having a volume average particle size of 1 μm or more and 4 μm or less exert a great influence on flowability and transfer efficiency of the toner. Therefore, it is necessary to design shapes of the toner particles having a volume average particle size of 1 μm or more and 4 μm or less, so as to obtain a toner excellent in flowability and transfer efficiency and to obtain a high-quality image sufficiently improved in definition and resolution.